Terrestrial television broadcast or radio broadcast often uses a plurality of antennas for transmitting same programs because the service area of a single broadcast wave is limited. If the broadcast waves transmitted from the respective antennas have a same frequency, interference can occur in any areas where two or more than two service areas overlap one another. Then, noise can arise in the received sound and a so-called “ghost phenomenon” of multiplexed images can occur.
In view of this problem of terrestrial broadcasting, broadcast waves are conventionally transmitted by using different frequencies for them particularly in adjacent service areas in order to avoid interference of broadcast waves. Thus, when a receiver of a conventional terrestrial broadcasting system is moved from the service area of an antenna to that of another, it has to be tuned in to the frequency of the broadcast wave of the service area where the receiver is currently located.
Meanwhile, in recent years, research efforts have been paid for commercializing digital terrestrial broadcasting utilizing the MPEG-2 Systems (ITU-T H.222.0, ISO/IEC 13818-1) which is a compression transmission standard for audio and video information.
Since digital terrestrial broadcasting is adapted to transmit high quality sounds and images much better than conventional analog terrestrial broadcasting, there is a strong demand for digital terrestrial broadcasting systems. Additionally, digital terrestrial broadcasting can transmit various data to be utilized by way of computers and information terminals beside audio and video information. In other words, it can be used to transmit variety of combinations of different contents to provide various broadcasting services.
In the field of digital terrestrial broadcasting utilizing the MPEG-2 Systems, each broadcast unit such as a news coverage or a drama that starts and ends at predetermined respective hours is referred to as event and a given succession of a plurality of events is referred to as service. Many services are transmitted in the form of a transport stream. In the following description, the term “service” is reworded by “program” in order to avoid confusion between “service” and “service area”.
Now, digital terrestrial broadcasting can be used by a same broadcaster to provide different programs in each service area because various contents can be combined and broadcast digitally with ease.
Then, if an audience enjoying an event being broadcast through a given channel in a service area moves into another service area, he or she may no longer be able to receive the event in the new service area. For instance, if an audience receiving a “cooking program” as an event transmitted through a given channel in a service area moves to an adjacent service area, he or she may now be forced to receive a “night base ball game coverage” transmitted through the same channel in the new service area.
Additionally, a plurality of affiliated broadcasters may broadcast a same event at a same time. However, if an audience receiving the event in a service area of a specific broadcaster moves into an adjacent service area where some other broadcaster is broadcasting the same event, he or she will have to carry out cumbersome operations for making his or her receiving set adapted to properly receive the broadcast of the event in that area. That is, the receiving set temporarily falls into the state in which it cannot receive the terrestrial broadcast signal. Then, the audience may stop receiving the terrestrial broadcast signal or switch to receive a terrestrial broadcast signal transmitted by another broadcaster.